Ceiling fans have long been recognized and used as an inexpensive way to provide movement of air within rooms of buildings. They can be simple to use and install, safe, and inexpensive to buy and run when compared to such alternatives as for example refrigerated and evaporative air conditioning units. They can often provide a surprisingly effective alternative to air conditioning as the air movement they generate can evaporate skin perspiration with a resulting cooling effect.
It is known to combine ceiling fans with lighting means, as firstly it is a common requirement to provide ceiling mounted light sources, and secondly it is convenient to provide a single power supply to operate a combined fan and light fitting.
Less commonly, it has also been known to provide a combined light fitting and ceiling fan with some form of folding or retracting blade arrangement. Le Velle has described three versions. U.S. Pat. No. 1,445,402 discloses a light fitting and ceiling fan in which blades move outwards under centrifugal force when the fan is switched on, and are retracted by springs when the fan is switched off. U.S. Pat. Nos. 1,458,348 and 2,079,942 disclose improved versions, in which (unlike the early version of U.S. Pat. No. 1,445,402) the inward and outward movements of the blades are synchronized. Synchronizing blade movement is important for preserving satisfactory balance of the rotating parts of the fan. More recently, a combined light fitting and ceiling fan has been disclosed by Villella (see international patent publication WO 2007/006096) with a concealed and simple blade movement synchronizing arrangement that lends itself to modern design.
A problem in the design of a combined light fitting and ceiling fan is to provide blades that when in use can provide useful air moving performance without requiring excessive power and that when not in use can fold into a reasonably compact overall form. The present invention addresses this problem.
A fan blade having a single axis of curvature may exhibit improved aerodynamic performance over a flat blade but is still less than optimum. The present invention seeks to further enhance aerodynamic performance by providing a combined ceiling fan and light fitting having blades which are retractable and have biaxial curvature. The term biaxial curvature means that the blades have a shape such that they would be generated by a surface of revolution or non-linear movement of a curved line rather than a straight line.
The invention disclosed herein provides a combination ceiling fan and light fitting which has the advantages of blades which have biaxial curvature thereby providing enhanced aerodynamic performance and the feature of being retractable so that they can fold into a compact overall form so that they are concealed.
References above and elsewhere in this specification to certain patents are not intended as or to be taken as admitting that anything therein forms a part of the common general knowledge in the art in any place.